The role of CGRP in the pathophysiology of migraine and efficacy of CGRP receptor antagonists as acute antimigraine drugs

Efficacy and Safety of Rimegepant for the Acute Treatment of Migraine: Evidence From Randomized Controlled Trials

Background

As one of the novel therapeutic drugs that targets Calcitonin gene-related peptide (CGRP), 75 mg rimegepant has been used for the acute management of migraine, which is one of the most common neurological diseases worldwide. Several clinical trials have been conducted to investigate the efficacy and safety of rimegepant for the acute management of migraine, but no systematic review of existing literature has been performed. We therefore performed a meta-analysis to investigate the efficacy and safety of rimegepant in treatment of patients with migraine.

Method

Pubmed, Embased, and Cochrane Library were searched from January 2001 to August 2019 for randomized controlled trials (RCTs). Four RCTs with 3,827 patients were finally included in our study.

Result

We pooled 3,827 patients from four RCTs, and the primary endpoints were freedom from pain, most bothersome symptom, and pain relief at 2 hr post dose. We found that 75 mg rimegepant led to significant freedom from pain (P < 0.001), pain relief (P < 0.001), and freedom from the most bothersome symptom (P < 0.001) at 2 hr post dose compared with the placebo. In addition, there was no statistically significant increase in adverse events compared with the placebo.

Conclusions

75 mg rimegepant had good efficacy and safety for acute treatment of migraine. Further studies are needed to compare the efficacy of rimegepant with traditional drugs for acute management of migraine.

Making Better Dose Decisions: Using Exposure-Response Modeling to Integrate Efficacy Outcome of Two Phase IIb Clinical Trials of Ubrogepant for Migraine Treatment

Ubrogepant (MK‐1602) is a novel, oral, calcitonin gene‐related peptide receptor antagonist in clinical development with positive phase III outcomes for acute treatment of migraine. This paper describes the population exposure‐response (E‐R) modeling and simulations, which were used to inform the phase III dose‐selection rationale, based on ~ 800 participants pooled across two phase IIb randomized dose‐finding clinical trials. The E‐R model describes the placebo and ubrogepant treatment effects based on migraine pain end points (2‐hour pain relief and 2‐hour pain freedom) at various dose levels. Sensitivity analyses were conducted to evaluate various assumptions of placebo response in light of the high placebo response observed in one phase II trial. A population pharmacokinetic model describing the effect of formulations was included in the E‐R simulation framework to assess potential dose implications of a formulation switch from phase II to phase III. Model‐based simulations predict that a dose of 25 mg or higher is likely to achieve significantly better efficacy than placebo with desirable efficacy levels. The understanding of E‐R helped support the dose selection for the phase III clinical trials.

Are Migraine With and Without Aura Really Different Entities?

Background: Migraine research is booming with the rapidly developing neuroimaging tools. Structural and functional alterations of the migrainous brain were detected with MRI. The outcome of a research study largely depends on the working hypothesis, on the chosen measurement approach and also on the subject selection. Against all evidence from the literature that migraine subtypes are different, most of the studies handle migraine with and without aura as one disease. Methods: Publications from PubMed database were searched for terms of "migraine with aura," "migraine without aura," "interictal," "MRI," "diffusion weighted MRI," "functional MRI," "compared to," "atrophy" alone and in combination. Conclusion: Only a few imaging studies compared the two subforms of the disease, migraine with aura, and without aura, directly. Functional imaging investigations largely agree that there is an increased activity/activation of the brain in migraine with aura as compared to migraine without aura. We propose that this might be the signature of cortical hyperexcitability. However, structural investigations are not equivocal. We propose that variable contribution of parallel, competing mechanisms of maladaptive plasticity and neurodegeneration might be the reason behind the variable results.

Evaluation of Galcanezumab for the Prevention of Episodic Migraine: The EVOLVE-1 Randomized Clinical Trial

Importance

Migraine is a disabling neurological disease characterized by severe headache attacks. Treatment options reduce migraine frequency for many patients, but adverse effects lead to discontinuation in many patients.

Objective

To demonstrate that galcanezumab is superior to placebo in the prevention of episodic migraine with or without aura.

Design, Setting, and Participants

The EVOLVE-1 (Evaluation of LY2951742 in the Prevention of Episodic Migraine 1) trial was a double-blind, randomized, placebo-controlled (January 11, 2016, to March 22, 2017) trial comparing galcanezumab (120 mg and 240 mg) vs placebo. Patients received treatments once monthly for 6 months (subcutaneous injection via prefilled syringe) and were followed up for 5 months after their last injection. It was a multicenter, clinic-based study involving 90 sites in North America. Participants in the study were adults (aged 18 to 65 years) with at least a 1-year history of migraine, 4 to 14 migraine headache days per month and a mean of at least 2 migraine attacks per month within the past 3 months, and were diagnosed prior to age 50 years. During the study, no other preventive medications were allowed. A total of 1671 patients were assessed; 809 did not meet study entry or baseline criteria, and 858 were included in the intent-to-treat population.

Interventions

Patients were randomized (2:1:1) to monthly placebo, galcanezumab, 120 mg, and galcanezumab, 240 mg.

Main Outcomes and Measures

The primary outcome was overall mean change from baseline in the number of monthly migraine headache days during the treatment period. Secondary measures included at least 50%, at least 75%, and 100% reduction in monthly migraine headache days, migraine headache days with acute medication use, and scores from the Migraine-Specific Quality of Life questionnaire, Patient Global Impression of Severity, and Migraine Disability Assessment. Treatment-emergent adverse events and serious adverse events were reported.

Results

Of the 1671 patients assessed, 858 (mean age, 40.7 years; 718 women [83.7%]) met study entry criteria and received at least 1 dose of investigational product. The primary objective was met for both galcanezumab doses; treatment with galcanezumab significantly reduced monthly migraine headache days (both P < .001) by 4.7 days (120 mg) and 4.6 days (240 mg) compared with placebo (2.8 days). All key secondary objectives were also significant after multiplicity adjustment. There were no meaningful differences between 120-mg and 240-mg doses of galcanezumab on measures of efficacy. Completion rate during treatment was high (81.9%; n = 718), and the incidence of discontinuation owing to adverse events was less than 5% across all treatment groups.

Conclusions and Relevance

Galcanezumab 120-mg and 240-mg monthly injections provided clinical benefits and improved functioning. The incidence rate of adverse events was low, demonstrating the favorable tolerability profile of galcanezumab.

Trial Registration

ClinicalTrials.gov Identifier: NCT02614183.

Functional Characterization of the Prejunctional Receptors Mediating the Inhibition by Ergotamine of the Rat Perivascular Sensory Peptidergic Drive

Calcitonin gene-related peptide (α-CGRP) released from perivascular sensory nerves induces decreases in diastolic blood pressure (DBP). Experimentally, this can be shown by spinal thoracic (T₉-T₁₂) electrical stimulation of these afferent fibers. Because ergotamine inhibits these neurogenic vascular responses and displays affinity for monoaminergic receptors that inhibit neurotransmitter release, we investigated whether this ergotamine-induced inhibition results from activation of serotonin 5-HT_1B/1D, dopamine D₂-like, and α₂-adrenergic receptors. Wistar rats were pithed and, under autonomic ganglion blockade, received intravenous infusions of methoxamine followed by ergotamine (0.1-3.1 μg kg^-1 min^-1). Thoracic T₉-T₁₂ electrical stimulation or an intravenous bolus of α-CGRP resulted in decreases in DBP. Ergotamine inhibited the electrically induced, but not α-CGRP-induced, responses. The vasodilator sensory inhibition by 3.1 μg of ergotamine kg^-1 min^-1 was resistant to simultaneous blockade of 5-HT_1B/1D, D₂-like, and α₂-adrenergic receptors upon addition of antagonists GR127935, haloperidol, and rauwolscine. Moreover, the inhibition by 0.31 μg of ergotamine kg^-1 min^-1 was unaltered by GR127935 and haloperidol, partly blocked by GR127935 and rauwolscine or rauwolscine and haloperidol, and abolished by GR127935, haloperidol, and rauwolscine. These findings imply that prejunctional 5-HT_1B/1D, D₂-like, and α₂-adrenergic receptors mediate the sensory inhibition induced by 0.31 μg of ergotamine kg^-1 min^-1, whereas larger doses may involve other receptors. Thus, ergotamine's ability to inhibit the perivascular sensory peptidergic drive may result in facilitation of its systemic vasoconstrictor properties.

The need for new acutely acting antimigraine drugs: moving safely outside acute medication overuse

Background

The treatment of migraine is impeded by several difficulties, among which insufficient headache relief, side effects, and risk for developing medication overuse headache (MOH). Thus, new acutely acting antimigraine drugs are currently being developed, among which the small molecule CGRP receptor antagonists, gepants, and the 5-HT_1F receptor agonist lasmiditan. Whether treatment with these drugs carries the same risk for developing MOH is currently unknown.

Main body

Pathophysiological studies on MOH in animal models have suggested that decreased 5-hydroxytryptamine (5-HT, serotonin) levels, increased calcitonin-gene related peptide (CGRP) expression and changes in 5-HT receptor expression (lower 5-HT_1B/D and higher 5-HT_2A expression) may be involved in MOH. The decreased 5-HT may increase cortical spreading depression frequency and induce central sensitization in the cerebral cortex and caudal nucleus of the trigeminal tract. Additionally, low concentrations of 5-HT, a feature often observed in MOH patients, could increase CGRP expression. This provides a possible link between the pathways of 5-HT and CGRP, targets of lasmiditan and gepants, respectively. Since lasmiditan is a 5-HT_1F receptor agonist and gepants are CGRP receptor antagonists, they could have different risks for developing MOH because of the different (over) compensation mechanisms following prolonged agonist versus antagonist treatment.

Conclusion

The acute treatment of migraine will certainly improve with the advent of two novel classes of drugs, i.e., the 5-HT_1F receptor agonists (lasmiditan) and the small molecule CGRP receptor antagonists (gepants). Data on the effects of 5-HT_1F receptor agonism in relation to MOH, as well as the effects of chronic CGRP receptor blockade, are awaited with interest.

Effect of Galcanezumab Following Treatment Cessation in Patients With Migraine: Results From 2 Randomized Phase 3 Trials

Objective

We examined the efficacy and safety of galcanezumab after treatment cessation in randomized double‐blind, placebo‐controlled, migraine prevention studies (EVOLVE‐1; EVOLVE‐2).

Background

Galcanezumab is indicated for migraine prevention in adults.

Methods

Adults with episodic migraine were enrolled into EVOLVE‐1 and EVOLVE‐2, which randomized 858 and 915 patients, respectively, to galcanezumab 120 mg (an initial 240‐mg loading dose), galcanezumab 240 mg, or placebo, administered subcutaneously once monthly for 6 months. After treatment completion or discontinuation, patients entered a 4‐month posttreatment period. Efficacy and safety from the posttreatment periods are reported.

Results

Overall, 740 patients (EVOLVE‐1) and 830 (EVOLVE‐2) patients entered the posttreatment periods, about 95% and 96% of patients, respectively, completed. In EVOLVE‐1, change from pre‐randomization baseline in monthly migraine headache days decreased over the posttreatment period from (mean [SE]) 5.2 (0.4) days (Month 6) to 4.1 (0.4) days (Month 10) for 120 mg and from 5.3 (0.4) days (Month 6) to 3.8 (0.4) days (Month 10) for 240 mg, and was stable for placebo (3.4 [0.3] days [Month 6] to 3.3 [0.3] days [Month 10]); differences between each galcanezumab dose group and placebo were statistically significant at each month, except for galcanezumab 240 mg at Month 10 (120 mg vs placebo: P < .001 Months 1‐6, P = .007 Month 7, P = .044 Month 8, P = .016 Month 9, and P = .042 Month 10; 240 mg vs placebo: P < .001 Months 1–7, P = .015 Month 8, P = .021 Month 9, and P = .238 Month 10). EVOLVE‐2 showed similar results. In both trials, there were no statistically significant differences between treatment groups and placebo for time‐to‐first loss of 50% response. During the posttreatment periods, 1.6% (EVOLVE‐1) and 2.3% (EVOLVE‐2) of patients initiated migraine preventive treatments. At Month 10, quality of life among galcanezumab‐treated patients was similar to those taking placebo. The most common posttreatment emergent adverse event was upper respiratory tract infections. There were no discontinuations due to adverse events during the posttreatment periods.

Conclusions

Galcanezumab treatment effects were reduced during the posttreatment periods, but did not return to baseline. There were no unexpected adverse events after galcanezumab cessation.

Circulating nociceptin and CGRP in medication-overuse headache

BACKGROUND

Previous studies found low serum levels of nociceptin in migraine patients but high serum levels of calcitonin gene-related peptide (CGRP). CGRP can elicit migraine-like headache. Medication-Overuse Headache (MOH) often has migraine features and can mimic chronic migraine. We therefore hypothesized that as in migraine, serum levels of nociceptin would be lower and CGRP serum levels higher in MOH patients compared with those in healthy volunteers. We hypothesized that the serum levels would normalize after detoxification.

METHODS

Seventeen MOH patients, hereof 70.6% with chronic migraine and MOH, and 30 sex and age matched headache-free controls were included. MOH patients underwent a 2-month outpatient detoxification program and after 6 months, 10 patients and 19 controls were retested. Blood samples were analyzed blinded.

RESULTS

We found no differences in the levels of nociceptin and CGRP between MOH patients and controls (P = 0.65 and P = 0.59). The mean headache frequency reduction was 43% and 70% of patients reverted to episodic headache after 6 months, but the levels of nociceptin and CGRP were unchanged (P = 0.71 and P = 0.82).

CONCLUSION

In contrast to previous findings in migraine patients, we found normal serum levels of nociceptin and CGRP in MOH patients. Thus, we find no evidence that the increased headache frequency of MOH patients could be caused by altered nociceptin and CGRP levels. This underlines the importance of identifying medication overuse in chronic headache and treating the MOH.

CGRP Is Critical for Hot Flushes in Ovariectomized Mice

Hot flushes are common and troublesome symptoms of menopause. The neuropeptide calcitonin gene-related peptide (CGRP) is increased in plasma during hot flushes but it has not been clear if CGRP is causally involved in the mechanism underpinning the flushes. Here, we examined the effect of interventions with CGRP in a mouse model of hot flushes based on flush-like temperature increases triggered by forced physical activity in ovariectomized mice. Compared to normal mice, ovariectomized mice reacted with an exaggerated, flush-like, temperature increase after physical exercise. This increase was completely blocked by the non-peptide CGRP-antagonist MK-8825 (-0.41 degrees Celsius, 95% CI: -0,83 to 0,012, p < 0.0001) at a dose that had no obvious effects on locomotor activity (50 mg/kg). Further, the flush-like temperature increases were strongly attenuated in ovariectomized mice lacking αCGRP due to a genetic modification. Collectively, our findings suggest that CGRP is an important mediator of experimentally induced hot flushes and they identify CGRP antagonists as promising treatment candidates for women and possibly also men with hot flushes.

Perampanel inhibits calcitonin gene-related peptide release from rat brainstem in vitro

Background

Perampanel is a novel antiepileptic drug acting via non-competitive antagonism on glutamatergic AMPA receptors, and the subsequent inhibition of ion calcium influx. Since it was recently postulated that the antagonists of glutamate receptors might play a role in the treatment of migraine, in this study we investigated the putative anti-migraine activity of perampanel in an in vitro animal model involving the static incubation of rat brainstem explants and the subsequent measurement of immune-reactive calcitonin gene-related peptide released into the incubation medium.

Methods

Acute rat brainstem explants were incubated in plain medium or in medium containing graded concentrations of perampanel. The release into the medium was assessed by radioimmunoassay either under baseline conditions or after stimulation by such secretagogues as high K⁺ concentrations, veratridine or capsaicin.

Results

We found that: 1) under baseline conditions perampanel, given in the range 0.01–100 μM, inhibited in a concentration-dependent manner calcitonin gene-related peptide’s release compared to controls; the decrease was statistically significant as from 10 μM; 2) a significant and consistent increase in calcitonin gene-related peptide’s secretion was induced by all depolarizing stimuli after 1 h of incubation; 3) under these conditions, calcitonin gene-related peptide’s release stimulated by 56 mM KCl was significantly reduced by perampanel from 0.1 μM onward, whereas secretion stimulated by veratridine was significantly reduced as from 1 μM; 4) on the contrary, perampanel had no effect on capsaicin-induced calcitonin gene-related peptide’s release up to 100 μM.

Conclusions

Here we provided preliminary in vitro evidence suggesting that perampanel might control pain transmission under conditions of activated trigeminal system, in a preclinical model mimicking the pathophysiology of human migraine.

Loss of α-Calcitonin Gene-Related Peptide (αCGRP) Reduces Otolith Activation Timing Dynamics and Impairs Balance

Calcitonin gene-related peptide (CGRP) is a neuroactive peptide that is thought to play a role at efferent synapses in hair cell organs including the cochlea, lateral line, and semicircular canal. The deletion of CGRP in transgenic mice is associated with a significant reduction in suprathreshold cochlear nerve activity and vestibulo–ocular reflex (VOR) gain efficacy when compared to littermate controls. Here we asked whether the loss of CGRP also influences otolithic end organ function and contributes to balance impairments. Immunostaining for CGRP was absent in the otolithic end organs of αCGRP null (-/-) mice while choline acetyltransferase (ChAT) immunolabeling appeared unchanged suggesting the overall gross development of efferent innervation in otolithic organs was unaltered. Otolithic function was assessed by quantifying the thresholds, suprathreshold amplitudes, and latencies of vestibular sensory-evoked potentials (VsEPs) while general balance function was assessed using a modified rotarod assay. The loss of αCGRP in null (-/-) mice was associated with: (1) shorter VsEP latencies without a concomitant change in amplitude or thresholds, and (2) deficits in the rotarod balance assay. Our findings show that CGRP loss results in faster otolith afferent activation timing, suggesting that the CGRP component of the efferent vestibular system (EVS) also plays a role in otolithic organ dynamics, which when coupled with reduced VOR gain efficacy, impairs balance.

Solid-Phase Thiol-Ene Lipidation of Peptides for the Synthesis of a Potent CGRP Receptor Antagonist

We report a new method herein coined SP-CLipPA (solid-phase cysteine lipidation of a peptide or amino acid) for the synthesis of mono-S-lipidated peptides. This technique utilizes thiol-ene chemistry for conjugation of a vinyl ester to a free thiol of a semiprotected, resin-bound peptide. Advantages of SP-CLipPA include: ease of handling, conversions of up to 91 %, by-product removal by simple filtration, and a single purification step. Additionally, the desired lipidated products show high chromatographic separation from impurities, thus facilitating RP-HPLC purification. To showcase the utility of SP-CLipPA, we synthesized a potent calcitonin gene-related peptide (CGRP) receptor antagonist peptide in excellent yield and purity. This peptide, selected from a series of lipidated analogues of CGRP_8-37 and CGRP_7-37 , has potential for the treatment of migraine.

Is selective 5-HT1F receptor agonism an entity apart from that of the triptans in antimigraine therapy?

Migraine is a neurovascular disorder that involves activation of the trigeminovascular system and cranial vasodilation mediated by release of calcitonin gene-related peptide (CGRP). The gold standard for acute migraine treatment are the triptans, 5-HT1B/1D/(1F) receptor agonists. Their actions are thought to be mediated through activation of: (i) 5-HT1B receptors in cranial blood vessels with subsequent cranial vasoconstriction; (ii) prejunctional 5-HT1D receptors on trigeminal fibers that inhibit trigeminal CGRP release; and (iii) 5-HT1B/1D/1F receptors in central nervous system involved in (anti)nociceptive modulation. Unfortunately, coronary arteries also express 5-HT1B receptors whose activation would produce coronary vasoconstriction; hence, triptans are contraindicated in patients with cardiovascular disease. In addition, since migraineurs have an increased cardiovascular risk, it is important to develop antimigraine drugs devoid of vascular (side) effects. Ditans, here defined as selective 5-HT1F receptor agonists, were developed on the basis that most of the triptans activate trigeminal 5-HT1F receptors, which may explain part of the triptans' antimigraine action. Amongst the ditans, lasmiditan: (i) fails to constrict human coronary arteries; and (ii) is effective for the acute treatment of migraine in preliminary Phase III clinical trials. Admittedly, the exact site of action is still unknown, but lasmiditan possess a high lipophilicity, which suggests a direct action on the central descending antinociceptive pathways. Furthermore, since 5-HT1F receptors are located on trigeminal fibers, they could modulate CGRP release. This review will be particularly focussed on the similarities and differences between the triptans and the ditans, their proposed sites of action, side effects and their cardiovascular risk profile.

Emerging Role of (Endo)Cannabinoids in Migraine

In this mini-review, we summarize recent discoveries and present new hypotheses on the role of cannabinoids in controlling trigeminal nociceptive system underlying migraine pain. Individual sections of this review cover key aspects of this topic, such as: (i) the current knowledge on the endocannabinoid system (ECS) with emphasis on expression of its components in migraine related structures; (ii) distinguishing peripheral from central site of action of cannabinoids, (iii) proposed mechanisms of migraine pain and control of nociceptive traffic by cannabinoids at the level of meninges and in brainstem, (iv) therapeutic targeting in migraine of monoacylglycerol lipase and fatty acid amide hydrolase, enzymes which control the level of endocannabinoids; (v) dual (possibly opposing) actions of cannabinoids via anti-nociceptive CB1 and CB2 and pro-nociceptive TRPV1 receptors. We explore the cannabinoid-mediated mechanisms in the frame of the Clinical Endocannabinoid Deficiency (CECD) hypothesis, which implies reduced tone of endocannabinoids in migraine patients. We further discuss the control of cortical excitability by cannabinoids via inhibition of cortical spreading depression (CSD) underlying the migraine aura. Finally, we present our view on perspectives of Cannabis-derived (extracted or synthetized marijuana components) or novel endocannabinoid therapeutics in migraine treatment.

Safety of galcanezumab in patients with episodic migraine: A randomized placebo-controlled dose-ranging Phase 2b study

Background Safety findings from a Phase 2b study of galcanezumab, a humanized monoclonal antibody against calcitonin gene-related peptide, for prevention of migraine (NCT02163993) are reported here. Methods Patients aged 18-65 years with episodic migraine were evaluated in this multicenter, double-blind, randomized study. After randomization, 410 patients were administered 5, 50, 120 or 300 mg of galcanezumab or placebo subcutaneously once every 4 weeks for 12 weeks, followed by a post-treatment off-drug period lasting 12 weeks. Results Treatment-emergent adverse events (TEAEs) were primarily rated as mild to moderate. Serious adverse events reported in galcanezumab dose groups were appendicitis, Crohn's disease, suicidal ideation, and congenital ankyloglossia in an infant of a paternal pregnancy; each of these were reported by one patient. Adverse events leading to discontinuation with galcanezumab treatment were abdominal pain, visual impairment, and upper limb fracture, each reported by one patient. Treatment-emergent injection-site reactions were reported significantly more frequently ( p = 0.013) with galcanezumab (13.9%) than with placebo (5.8%). Injection-site pain was the most common injection-site reaction (galcanezumab 11.4%; placebo 2.9%, p = 0.004). Upper respiratory tract infection (galcanezumab 10.0%; placebo 8.8%) and nasopharyngitis (galcanezumab 7.0%; placebo 2.2%) also occurred more frequently with galcanezumab treatment. Potential hypersensitivity events were reported at similar frequencies in galcanezumab (3.3%) and placebo (5.1%) groups. Incidence of treatment-emergent anti-drug antibodies in galcanezumab dose groups (4.6% of patients during treatment period) did not appear to have any meaningful effects on safety, the pharmacokinetics of galcanezumab, or its ability to bind to the target ligand. Conclusion The results from this 3-month Phase 2b study support the initiation of larger Phase 3 trials of longer duration.

Side effects associated with current and prospective antimigraine pharmacotherapies

INTRODUCTION

Migraine is a neurovascular disorder. Current acute specific antimigraine pharmacotherapies target trigeminovascular 5-HT1B/1D, 5-HT1F and CGRP receptors but, unfortunately, they induce some cardiovascular and central side effects that lead to poor treatment adherence/compliance. Therefore, new antimigraine drugs are being explored. Areas covered: This review considers the adverse (or potential) side effects produced by current and prospective antimigraine drugs, including medication overuse headache (MOH) produced by ergots and triptans, the side effects observed in clinical trials for the new gepants and CGRP antibodies, and a section discussing the potential effects resulting from disruption of the cardiovascular CGRPergic neurotransmission. Expert opinion: The last decades have witnessed remarkable developments in antimigraine therapy, which includes acute (e.g. triptans) and prophylactic (e.g. β-adrenoceptor blockers) antimigraine drugs. Indeed, the triptans represent a considerable advance, but their side effects (including nausea, dizziness and coronary vasoconstriction) preclude some patients from using triptans. This has led to the development of the ditans (5-HT1F receptor agonists), the gepants (CGRP receptor antagonists) and the monoclonal antibodies against CGRP or its receptor. The latter drugs represent a new hope in the antimigraine armamentarium, but as CGRP plays a role in cardiovascular homeostasis, the potential for adverse cardiovascular side effects remains latent.

The effect and safety of monoclonal antibodies to calcitonin gene-related peptide and its receptor on migraine: a systematic review and meta-analysis

BACKGROUND

Migraine has been recognized as one of the leading causes of disability in the 2013 Global Burden of Disease Study and seriously affects the quality of patients' life, current treatment options are not ideal. Monoclonal antibodies to calcitonin gene-related peptide and its receptor (CGRP-mAbs) appear more promising for migraine because of considerably better effect and safety profiles. The objective of this study is to systematically assess the clinical efficacy and safety of CGRP-mAbs for migraine therapy.

METHODS

A systematic literature search in PubMed, Cochrane Library and Baidu Scholar was performed to identify randomized controlled trials (RCTs), which compared the effect and safety of CGRP-mAbs with placebo on migraine. Regarding the efficacy, the reduction of monthly migraine days from baseline to weeks 1-4, 5-8, and 9-12; responder rates were extracted as the outcome measures of the effects of CGRP-mAbs. Regarding the safety, total adverse events, the main adverse events, and other adverse events were evaluated.

RESULTS

We found significant reduction of monthly migraine days in CGRP-mAbs vs. placebo (weeks 1-4: SMD -0.49, 95% CI -0.61 to -0.36; weeks 5-8: SMD -0.43, 95% CI -0.56 to -0.30; weeks 9-12: SMD -0.37, 95% CI -0.49 to -0.24). 50% and 75% responder rates (OR 2.59, 95% CI 1.99 to 3.37; and OR 2.91, 95% CI 2.06 to 4.10) were significantly increased compared with placebo. There was no significant difference in total adverse events (OR 1.17, 95% CI 0.91 to 1.51), and the main adverse events including upper respiratory tract infection (OR 1.44, 95% CI 0.82 to 2.55), nasopharyngitis (OR 0.59, 95% CI 0.30 to 1.16), nausea (OR 0.61, 95% CI 0.29 to 1.32), injection-site pain (OR 1.73, 95% CI 0.95 to 3.16) and back pain (OR 0.97, 95% CI 0.49 to 1.90) were not obviously changed compared with placebo control, but the results showed significant increase of dizziness in CGRP-mAbs vs. placebo (OR 3.22, 95% CI 1.09 to 9.45).

CONCLUSIONS

This meta-analysis suggests that CGRP-mAbs are effective in anti-migraine therapy with few adverse reactions, but more and larger sample-size RCTs are required to verify the current findings.

Triptans and CGRP blockade - impact on the cranial vasculature

The trigeminovascular system plays a key role in the pathophysiology of migraine. The activation of the trigeminovascular system causes release of various neurotransmitters and neuropeptides, including serotonin and calcitonin gene-related peptide (CGRP), which modulate pain transmission and vascular tone. Thirty years after discovery of agonists for serotonin 5-HT1B and 5-HT1D receptors (triptans) and less than fifteen after the proof of concept of the gepant class of CGRP receptor antagonists, we are still a long way from understanding their precise site and mode of action in migraine. The effect on cranial vasculature is relevant, because all specific anti-migraine drugs and migraine pharmacological triggers may act in perivascular space. This review reports the effects of triptans and CGRP blocking molecules on cranial vasculature in humans, focusing on their specific relevance to migraine treatment.

The KATP channel in migraine pathophysiology: a novel therapeutic target for migraine

BACKGROUND

To review the distribution and function of KATP channels, describe the use of KATP channels openers in clinical trials and make the case that these channels may play a role in headache and migraine.

DISCUSSION

KATP channels are widely present in the trigeminovascular system and play an important role in the regulation of tone in cerebral and meningeal arteries. Clinical trials using synthetic KATP channel openers report headache as a prevalent-side effect in non-migraine sufferers, indicating that KATP channel opening may cause headache, possibly due to vascular mechanisms. Whether KATP channel openers can provoke migraine in migraine sufferers is not known.

CONCLUSION

We suggest that KATP channels may play an important role in migraine pathogenesis and could be a potential novel therapeutic anti-migraine target.

Olcegepant blocks neurogenic and non-neurogenic CGRPergic vasodepressor responses and facilitates noradrenergic vasopressor responses in pithed rats

BACKGROUND AND PURPOSE

Olcegepant (BIBN4096BS) is a selective non-peptide CGRP receptor antagonist with acute antimigraine properties. Since systemic vascular tone is modulated by perivascular (primary sensory CGRPergic and sympathetic) nerves, this randomized study investigated in pithed rats the effect of acute i.v. treatment with olcegepant on the neurogenic and non-neurogenic: (i) CGRPergic vasodepressor responses; and (ii) noradrenergic vasopressor responses. The pithed rat is an experimental model predictive of systemic (cardio) vascular side effects.

EXPERIMENTAL APPROACH

Seventy-five male Wistar rats (divided into 15 groups, n = 5 each) were pithed, artificially ventilated and prepared for: (i) spinal stimulation (T₉ -T₁₂ ; 0.56-5.6 Hz) of the sensory CGRPergic vasodepressor outflow or i.v. bolus injections (0.1-1 μg·kg^-1 ) of α-CGRP, substance P or acetylcholine, which induced frequency-dependent or dose-dependent vasodepressor responses; or (ii) spinal stimulation (T₇ -T₉ ; 0.03-3 Hz) of the sympathetic vasopressor outflow or i.v. bolus injections (0.03-3 μg·kg^-1 ) of noradrenaline, which produced frequency-dependent or dose-dependent vasopressor responses.

KEY RESULTS

Olcegepant (1000 and 3000 μg·kg^-1 , i.v.) dose-dependently blocked the vasodepressor responses to sensory nerve stimulation or i.v. α-CGRP, without affecting those to substance P or acetylcholine. Whereas it potentiated the vasopressor responses to sympathetic nerve stimulation or i.v. noradrenaline.

CONCLUSIONS AND IMPLICATIONS

Olcegepant (i.v.) selectively blocked the neurogenic and non-neurogenic CGRPergic vasodepressor responses. This blockade by olcegepant potentiated the neurogenic and non-neurogenic noradrenergic vasopressor responses in pithed rats, an effect that might result in an increased vascular resistance and, consequently, in a prohypertensive action.

CGRP receptor activity in mice with global expression of human receptor activity modifying protein 1

BACKGROUND AND PURPOSE

CGRP is a potent vasodilator and nociceptive neuropeptide linked to migraine. CGRP receptors are heterodimers of receptor activity modifying protein 1 (RAMP1) and either calcitonin receptor-like receptor (CLR; forms canonical CGRP receptor) or calcitonin receptor (CT receptor; forms AMY₁ receptor). The goal of this study was to test whether transgenic mice globally expressing human RAMP1 have increased CGRP receptor activity and whether the receptors are sensitive to human selective antagonist telcagepant.

EXPERIMENTAL APPROACH

cAMP production was measured in primary cultures of aortic smooth muscle and trigeminal ganglia neurons from global hRAMP1 mice and non-transgenic littermates. Functional activity and inhibition were compared with clonal cell lines expressing combinations of CLR or CT receptors with RAMP1.

KEY RESULTS

Cultured smooth muscle from global hRAMP1 mice had a 10-fold greater CGRP-induced cAMP maximal response (Rmax) than non-transgenic littermates, with similar EC₅₀ s. In contrast, cultured trigeminal ganglia from global hRAMP1 mice had a 40-fold leftward shift of the EC₅₀ , with similar Rmax values as littermates. In both hRAMP1 cultures, telcagepant blocked CGRP-induced cAMP production, but was not effective in non-transgenic cultures. IC₅₀ values were closer to those observed for CT receptor/hRAMP1 than CLR/hRAMP1 in clonal cell lines.

CONCLUSIONS AND IMPLICATIONS

Overexpression of hRAMP1 increases CGRP signalling by changing the maximal response or ligand sensitivity, depending on tissue type. Furthermore, telcagepant inhibited transgenic hRAMP1 CGRP receptors, but the degree of inhibition suggests that the transgenic mice are only partially humanized or both canonical CGRP and AMY₁ receptors are functional in trigeminal ganglia neurons and vascular smooth muscle.

CGRP and its receptors

The calcitonin gene-related peptide (CGRP) neuropeptide system is an important but still evolving target for migraine. A fundamental consideration for all of the current drugs in clinical trials and for ongoing development in this area is the identity, expression pattern, and function of CGRP receptors because this knowledge informs safety and efficacy considerations. In recent years, only the calcitonin receptor-like receptor/receptor activity-modifying protein 1 (RAMP1) complex, known as the CGRP receptor, has generally been considered relevant. However, CGRP is capable of activating multiple receptors and could have more than one endogenous receptor. The recent identification of the CGRP-responsive calcitonin receptor/RAMP1 complex (AMY₁ receptor - amylin subtype 1 receptor) in the trigeminovascular system warrants a deeper consideration of the molecular identity of CGRP receptor(s) involved in the pathophysiology, and thus potential treatment of migraine. This perspective considers some of the issues and implications.

Diverse Physiological Roles of Calcitonin Gene-Related Peptide in Migraine Pathology: Modulation of Neuronal-Glial-Immune Cells to Promote Peripheral and Central Sensitization

The neuropeptide calcitonin gene-related peptide (CGRP) is implicated in the underlying pathology of migraine by promoting the development of a sensitized state of primary and secondary nociceptive neurons. The ability of CGRP to initiate and maintain peripheral and central sensitization is mediated by modulation of neuronal, glial, and immune cells in the trigeminal nociceptive signaling pathway. There is accumulating evidence to support a key role of CGRP in promoting cross excitation within the trigeminal ganglion that may help to explain the high co-morbidity of migraine with rhinosinusitis and temporomandibular joint disorder. In addition, there is emerging evidence that CGRP facilitates and sustains a hyperresponsive neuronal state in migraineurs mediated by reported risk factors such as stress and anxiety. In this review, the significant role of CGRP as a modulator of the trigeminal system will be discussed to provide a better understanding of the underlying pathology associated with the migraine phenotype.

Heteroreceptors Modulating CGRP Release at Neurovascular Junction: Potential Therapeutic Implications on Some Vascular-Related Diseases

Calcitonin gene-related peptide (CGRP) is a 37-amino-acid neuropeptide belonging to the calcitonin gene peptide superfamily. CGRP is a potent vasodilator with potential therapeutic usefulness for treating vascular-related disease. This peptide is primarily located on C- and Aδ-fibers, which have extensive perivascular presence and a dual sensory-efferent function. Although CGRP has two major isoforms (α-CGRP and β-CGRP), the α-CGRP is the isoform related to vascular actions. Release of CGRP from afferent perivascular nerve terminals has been shown to result in vasodilatation, an effect mediated by at least one receptor (the CGRP receptor). This receptor is an atypical G-protein coupled receptor (GPCR) composed of three functional proteins: (i) the calcitonin receptor-like receptor (CRLR; a seven-transmembrane protein), (ii) the activity-modifying protein type 1 (RAMP1), and (iii) a receptor component protein (RCP). Although under physiological conditions, CGRP seems not to play an important role in vascular tone regulation, this peptide has been strongly related as a key player in migraine and other vascular-related disorders (e.g., hypertension and preeclampsia). The present review aims at providing an overview on the role of sensory fibers and CGRP release on the modulation of vascular tone.

CGRP and Visceral Pain: The Role of Sex Hormones in In Vitro Experiment

A large number of studies have showed that women reported feeling pain more acutely than men. In support of this hypothesis, many research groups proved that in different animals model of pain the sex hormones regulate the somatic and visceral sensitivity to different noxious stimuli. Therefore, in this study, we went to evaluate if estrogen hormones by regulating the CGRP levels are implicated during the visceral pain transmission. Toward this aim, we have investigated the effect of 17β-estradiol in regulating the synthesis and release of CGRP, as well as the expression levels of the opioid receptor of type K. In order to gain information about the potential effects of 17β-estradiol on K-opioid receptor expression and activity, we have cultured F11 cells. Our results revealed that, when F11 cells were short-term exposed (30 min) to 17β-estradiol, the expression of the opioid K receptor was not significantly modified. We carried out enzyme immunoassay analysis to evaluate the potential effects of short-term exposure to 17-estradiol (30 min) on the release of CGRP in F11 cells. The results obtained showed that 17β-estradiol at the dose of 100 nM is able to induce the release of CGRP from F11 cells; whereas, a higher dose of 17β-estradiol (200 nM) did not produce significant effects when compared to control. In conclusion, all these findings suggest that the 17β-estradiol-regulated release of CGRP could at least in part provide a rational explanation for the difference of gender in the visceral pain sensitivity. J. Cell. Biochem. 118: 510-517, 2017. © 2016 Wiley Periodicals, Inc.

Calcitonin gene-related peptide induced migraine attacks in patients with and without familial aggregation of migraine

Background

Calcitonin gene-related peptide provokes migraine attacks in 65% of patients with migraine without aura. Whether aggregation of migraine in first-degree relatives (family load) or a high number of risk-conferring single nucleotide polymorphisms contributes to migraine susceptibility to calcitonin gene-related peptide infusion in migraine patients is unknown. We hypothesized that genetic enrichment plays a role in triggering of migraine and, therefore, migraine without aura patients with high family load would report more migraine attacks after calcitonin gene-related peptide infusion than patients with low family load.

Methods

We allocated 40 previously genotyped migraine without aura patients to receive intravenous infusion of 1.5 µg/min calcitonin gene-related peptide and recorded migraine attacks including headache characteristics and associated symptoms. Information of familial aggregation was obtained by telephone interview of first-degree relatives using a validated semi-structured questionnaire.

Results

Calcitonin gene-related peptide infusion induced a migraine-like attack in 75% (12 out of 16) of patients with high family load compared to 52% (12 out of 23) with low family load ( P = 0.150). In addition, we found that the migraine response after calcitonin gene-related peptide was not associated with specific or a high number of risk-conferring single nucleotide polymorphisms of migraine without aura.

Conclusion

We found no statistical association between familial aggregation of migraine and hypersensitivity to calcitonin gene-related peptide infusion in migraine without aura patients. We also demonstrated that the currently known single nucleotide polymorphisms conferring risk of migraine without aura have no additive effect on calcitonin gene-related peptide induced migraine-like attacks.

Migraine in the era of precision medicine

Migraine is a common neurovascular disorder in the neurologic clinics whose mechanisms have been explored for several years. The aura has been considered to be attributed to cortical spreading depression (CSD) and dysfunction of the trigeminovascular system is the key factor that has been considered in the pathogenesis of migraine pain. Moreover, three genes (CACNA1A, ATP1A2, and SCN1A) have come from studies performed in individuals with familial hemiplegic migraine (FHM), a monogenic form of migraine with aura. Therapies targeting on the neuropeptids and genes may be helpful in the precision medicine of migraineurs. 5-hydroxytryptamine (5-HT) receptor agonists and calcitonin gene-related peptide (CGRP) receptor antagonists have demonstrated efficacy in the acute specific treatment of migraine attacks. Therefore, ongoing and future efforts to find new vulnerabilities of migraine, unravel the complexity of drug therapy, and perform biomarker-driven clinical trials are necessary to improve outcomes for patients with migraine.

Expression of calcitonin gene-related peptide, adenosine A2a receptor and adenosine A1 receptor in experiment rat migraine models

A migraine is a disabling neurovascular disorder characterized by a unilateral throbbing headache that lasts from 4 to 72 h. The headache is often accompanied by nausea, vomiting, phonophobia and photophobia, and may be worsened by physical exercise. The trigeminovascular system (TVS) is speculated to have an important role in migraines, although the pathophysiology of this disorder remains to be elucidated. Trigeminal ganglion (TG) and spinal trigeminal nucleus caudalis (TNC) are important components of the TVS. Several clinical cases have provided evidence for the involvement of the brainstem in migraine initiation. Electrical stimulation of the trigeminal ganglion (ESTG) in rats can activate TVS during a migraine attack. Calcitonin gene-related peptide (CGRP) is an important vasoactive compound produced following TVS activation. Numerous studies have revealed that adenosine and its receptors have an important role in pain transmission and regulation process. However, only a few studies have examined whether adenosine A2a receptor (A2aR) and adenosine A1 receptor (A1R) are involved in migraine and nociceptive pathways. In the present study, CGRP, A2aR and A1R expression levels were detected in the TG and TNC of ESTG models through reverse transcription-quantitative polymerase chain reaction and western blot analysis. Tianshu capsule (TSC), a type of Chinese medicine, was also used in the ESTG rat models to examine its influence on the three proteins. Results demonstrated that CGRP, A2aR and A1R mediated pain transmission and the regulation process during migraine and the expression of the three proteins was regulated by TSC.

New therapeutic approaches for the prevention and treatment of migraine

The management of patients with migraine is often unsatisfactory because available acute and preventive therapies are either ineffective or poorly tolerated. The acute treatment of migraine attacks has been limited to the use of analgesics, combinations of analgesics with caffeine, ergotamines, and the triptans. Successful new approaches for the treatment of acute migraine target calcitonin gene-related peptide (CGRP) and serotonin (5-hydroxytryptamine, 5-HT1F) receptors. Other approaches targeting the transient receptor potential vanilloid (TRPV1) receptor, glutamate, GABAA receptors, or a combination of 5-HT1B/1D receptors and neuronal nitric oxide synthesis have been investigated but have not been successful in clinical trials thus far. In migraine prevention, the most promising new approaches are humanised antibodies against CGRP or the CGRP receptor. Non-invasive and invasive neuromodulation approaches also show promise as both acute and preventive therapies, although further studies are needed to define appropriate candidates for these therapies and optimum protocols for their use.

Development of anti-migraine therapeutics using the capsaicin-induced dermal blood flow model

The efficacy of calcitonin gene-related peptide (receptor) (CGRP-(R)) blocking therapeutics in the treatment of acute migraine headache provided proof-of-concept for the involvement of CGRP in the pathophysiology of this disorder. One of the major hurdles for the development of any class of drugs, including CGRP blocking therapeutics, is the early clinical development process during which toxic and inefficacious compounds need to be eliminated as early as possible in order to focus on the most promising molecules. At this stage, human models providing proof of target engagement, combined with safety and tolerability studies, are extremely valuable in focusing on those therapeutics that have the highest engagement from the lowest exposure. They guide the go/no-go decision making, establish confidence in the candidate molecule by de-risking toxicity and safety issues and thereby speed up the early clinical development. In this review the focus is on the so called 'capsaicin model' as a typical example of a target engagement biomarker used as a human model for the development of CGRP blocking therapeutics. By applying capsaicin onto the skin, TRPV1 channels are activated and a CGRP-mediated increase in dermal blood flow can be quantified with laser Doppler perfusion imaging. Effective CGRP blocking therapeutics in turn, display blockade of this response. The translation of this biomarker model from animals to humans is discussed as well as the limitations of the assay in predicting the efficacy of anti-migraine drugs.

Episodic and chronic migraine headache: breaking down barriers to optimal treatment and prevention

Migraine is a common disabling primary headache disorder that affects an estimated 36 million Americans. Migraine headaches often occur over many years or over an individual's lifetime. By definition, episodic migraine is characterized by headaches that occur on fewer than 15 days per month. According to the recent International Classification of Headache Disorders (third revision) beta diagnostic criteria, chronic migraine is defined as "headaches on at least 15 days per month for at least 3 months, with the features of migraine on at least 8 days per month." However, diagnostic criteria distinguishing episodic from chronic migraine continue to evolve. Persons with episodic migraine can remit, not change, or progress to high-frequency episodic or chronic migraine over time. Chronic migraine is associated with a substantially greater personal and societal burden, more frequent comorbidities, and possibly with persistent and progressive brain abnormalities. Many patients are poorly responsive to, or noncompliant with, conventional preventive therapies. The primary goals of migraine treatment include relieving pain, restoring function, and reducing headache frequency; an additional goal may be preventing progression to chronic migraine. Although all migraineurs require abortive treatment, and all patients with chronic migraine require preventive treatment, there are no definitive guidelines delineating which persons with episodic migraine would benefit from preventive therapy. Five US Food and Drug Association strategies are approved for preventing episodic migraine, but only injections with onabotulinumtoxinA are approved for preventing chronic migraine. Identifying persons who require migraine prophylaxis and selecting and initiating the most appropriate treatment strategy may prevent progression from episodic to chronic migraine and alleviate the pain and suffering associated with frequent migraine.

CGRP as a neuropeptide in migraine: lessons from mice

Migraine is a neurological disorder that is far more than just a bad headache. A hallmark of migraine is altered sensory perception. A likely contributor to this altered perception is the neuropeptide calcitonin gene-related peptide (CGRP). Over the past decade, CGRP has become firmly established as a key player in migraine. Although the mechanisms and sites of action by which CGRP might trigger migraine remain speculative, recent advances with mouse models provide some hints. This brief review focuses on how CGRP might act as both a central and peripheral neuromodulator to contribute to the migraine-like symptom of light aversive behaviour in mice.

Comprehensive Review of Medicinal Marijuana, Cannabinoids, and Therapeutic Implications in Medicine and Headache: What a Long Strange Trip It's Been …

BACKGROUND

The use of cannabis, or marijuana, for medicinal purposes is deeply rooted though history, dating back to ancient times. It once held a prominent position in the history of medicine, recommended by many eminent physicians for numerous diseases, particularly headache and migraine. Through the decades, this plant has taken a fascinating journey from a legal and frequently prescribed status to illegal, driven by political and social factors rather than by science. However, with an abundance of growing support for its multitude of medicinal uses, the misguided stigma of cannabis is fading, and there has been a dramatic push for legalizing medicinal cannabis and research. Almost half of the United States has now legalized medicinal cannabis, several states have legalized recreational use, and others have legalized cannabidiol-only use, which is one of many therapeutic cannabinoids extracted from cannabis. Physicians need to be educated on the history, pharmacology, clinical indications, and proper clinical use of cannabis, as patients will inevitably inquire about it for many diseases, including chronic pain and headache disorders for which there is some intriguing supportive evidence.

OBJECTIVE

To review the history of medicinal cannabis use, discuss the pharmacology and physiology of the endocannabinoid system and cannabis-derived cannabinoids, perform a comprehensive literature review of the clinical uses of medicinal cannabis and cannabinoids with a focus on migraine and other headache disorders, and outline general clinical practice guidelines.

CONCLUSION

The literature suggests that the medicinal use of cannabis may have a therapeutic role for a multitude of diseases, particularly chronic pain disorders including headache. Supporting literature suggests a role for medicinal cannabis and cannabinoids in several types of headache disorders including migraine and cluster headache, although it is primarily limited to case based, anecdotal, or laboratory-based scientific research. Cannabis contains an extensive number of pharmacological and biochemical compounds, of which only a minority are understood, so many potential therapeutic uses likely remain undiscovered. Cannabinoids appear to modulate and interact at many pathways inherent to migraine, triptan mechanisms ofaction, and opiate pathways, suggesting potential synergistic or similar benefits. Modulation of the endocannabinoid system through agonism or antagonism of its receptors, targeting its metabolic pathways, or combining cannabinoids with other analgesics for synergistic effects, may provide the foundation for many new classes of medications. Despite the limited evidence and research suggesting a role for cannabis and cannabinoids in some headache disorders, randomized clinical trials are lacking and necessary for confirmation and further evaluation.

Migraine pathophysiology: lessons from mouse models and human genetics

Migraine is a common, disabling, and undertreated episodic brain disorder that is more common in women than in men. Unbiased genome-wide association studies have identified 13 migraine-associated variants pointing at genes that cluster in pathways for glutamatergic neurotransmission, synaptic function, pain sensing, metalloproteinases, and the vasculature. The individual pathogenetic contribution of each gene variant is difficult to assess because of small effect sizes and complex interactions. Six genes with large effect sizes were identified in patients with rare monogenic migraine syndromes, in which hemiplegic migraine and non-hemiplegic migraine with or without aura are part of a wider clinical spectrum. Transgenic mouse models with human monogenic-migraine-syndrome gene mutations showed migraine-like features, increased glutamatergic neurotransmission, cerebral hyperexcitability, and enhanced susceptibility to cortical spreading depression, which is the electrophysiological correlate of aura and a putative trigger for migraine. Enhanced susceptibility to cortical spreading depression increased sensitivity to focal cerebral ischaemia, and blocking of cortical spreading depression improved stroke outcome in these mice. Changes in female hormone levels in these mice modulated cortical spreading depression susceptibility in much the same way that hormonal fluctuations affect migraine activity in patients. These findings confirm the multifactorial basis of migraine and might allow new prophylactic options to be developed, not only for migraine but potentially also for migraine-comorbid disorders such as epilepsy, depression, and stroke.

Meningeal afferent signaling and the pathophysiology of migraine

Migraine is the most common neurological disorder. Attacks are complex and consist of multiple phases but are most commonly characterized by intense, unilateral, throbbing headache. The pathophysiology contributing to migraine is poorly understood and the disorder is not well managed with currently available therapeutics, often rendering patients disabled during attacks. The mechanisms most likely to contribute to the pain phase of migraine require activation of trigeminal afferent signaling from the cranial meninges and subsequent relay of nociceptive information into the central nervous system in a region of the dorsal brainstem known as the trigeminal nucleus caudalis. Events leading to activation of meningeal afferents are unclear, but nerve endings within this tissue are mechanosensitive and also express a variety of ion channels including acid-sensing ion channels and transient receptor-potential channels. These properties may provide clues into the pathophysiology of migraine by suggesting that decreased extracellular pH and environmental irritant exposure in the meninges contributes to headache. Neuroplasticity is also likely to play a role in migraine given that attacks are triggered by routine events that are typically nonnoxious in healthy patients and clear evidence of sensitization occurs during an attack. Where and how plasticity develops is also not clear but may include events directly on the afferents and/or within the TNC. Among the mediators potentially contributing to plasticity, calcitonin gene-related peptide has received the most attention within the migraine field but other mechanisms may also contribute. Ultimately, greater understanding of the molecules and mechanisms contributing to migraine will undoubtedly lead to better therapeutics and relief for the large number of patients across the globe who suffer from this highly disabling neurological disorder.

Serum MicroRNA Signatures in Migraineurs During Attacks and in Pain-Free Periods

MicroRNAs have emerged as important biomarkers and modulators of pathophysiological processes including oncogenesis and neurodegeneration. MicroRNAs are found to be involved in the generation and maintenance of pain in animal models of inflammation and neuropathic pain. Recently, microRNA dysregulation has been reported in patients with painful conditions such as complex regional pain syndrome and fibromyalgia. The aim of this study was to assess whether serum microRNA alterations occur during migraine attacks and whether migraine manifests in chronic serum microRNA aberrations. Two cohorts of 24 migraineurs, and age- and sex-matched healthy controls were included. High-content serum microRNA (miRNA) arrays were used to assess the serum microRNA profiles of migraineurs during attacks and pain-free periods in comparison with healthy controls. Of the 372 assessed microRNAs, 32 or ≈ 8% were found to be differentially expressed and 4 of these--miR-34a-5p, 29c-5p, -382-5p, and -26b-3p--were selected for further investigation. Migraine attacks were associated with an acute upregulation in miR-34a-5p and miR-382-5p expression. Interestingly, miR-382-5p not only exhibited an upregulation during attack but also proved to be a biomarker for migraine when comparing migraineurs in pain-free periods to the healthy control group (p = <0.01). In conclusion, migraine manifestation is reflected in serum miRNA aberrations, both during attacks and pain-free periods. This finding sheds light on the potential role of microRNAs in the pathophysiology of migraine and adds a new approach towards potential identification of much sought-after serum biomarkers of migraine.

Inhibitory effect of chronic oral treatment with fluoxetine on capsaicin-induced external carotid vasodilatation in anaesthetised dogs

Background

During migraine, capsaicin-sensitive trigeminal sensory nerves release calcitonin gene-related peptide (CGRP), resulting in cranial vasodilatation and central nociception. Moreover, 5-HT is involved in the pathophysiology of migraine and depression. Interestingly, some limited lines of evidence suggest that fluoxetine may be effective in migraine prophylaxis, but the underlying mechanisms are uncertain. Hence, this study investigated the canine external carotid vasodilator responses to capsaicin, α-CGRP and acetylcholine before and after acute and chronic oral treatment with fluoxetine.

Methods

Forty-eight vagosympathectomised male mongrel dogs were prepared to measure blood pressure, heart rate and external carotid blood flow. The thyroid artery was cannulated for infusions of agonists. In 16 of these dogs, a spinal cannula was inserted (C1–C3) for infusions of 5-HT.

Results

The external carotid vasodilator responses to capsaicin, α-CGRP and acetylcholine remained unaffected after intracarotid or i.v. fluoxetine. In contrast, the vasodilator responses to capsaicin, but not those to α-CGRP or acetylcholine, were inhibited after chronic oral treatment with fluoxetine (300 µg/kg; for 90 days) or intrathecal 5-HT.

Conclusions

Chronic oral fluoxetine inhibited capsaicin-induced external carotid vasodilatation, and this inhibition could partly explain its potential prophylactic antimigraine action.

Central Integration of Canal and Otolith Signals is Abnormal in Vestibular Migraine

Vestibular migraine (VM), a common cause of vestibular symptoms within the general population, is a disabling and poorly understood form of dizziness. We sought to examine the underlying pathophysiology of VM with three studies, which involved the central synthesis of canal and otolith cues, and present preliminary results from each of these studies: (1) VM patients appear to have reduced motion perception thresholds when canal and otolith signals are modulated in a co-planar manner during roll tilt; (2) percepts of roll tilt appear to develop more slowly in VM patients than in control groups during a centrifugation paradigm that presents conflicting, orthogonal canal and otolith cues; and (3) eye movement responses appear to be different in VM patients when studied with a post-rotational tilt paradigm, which also presents a canal–otolith conflict, as the shift of the eye’s rotational axis was larger in VM and the relationship between the axis shift and tilt suppression of the vestibulo-ocular reflex differed in VM patients relative to control groups. Based on these preliminary perceptual and eye movement results obtained with three different motion paradigms, we present a hypothesis that the integration of canal and otolith signals by the brain is abnormal in VM and that this abnormality could be cerebellar in origin. We provide potential mechanisms that could underlie these observations, and speculate that one of more of these mechanisms contributes to the vestibular symptoms and motion intolerance that are characteristic of the VM syndrome.

Calcitonin gene-related peptide (CGRP): a new target for migraine

Migraine is a neurological disorder that manifests as a debilitating headache associated with altered sensory perception. The neuropeptide calcitonin gene-related peptide (CGRP) is now firmly established as a key player in migraine. Clinical trials carried out during the past decade have proved that CGRP receptor antagonists are effective for treating migraine, and antibodies to the receptor and CGRP are currently under investigation. Despite this progress in the clinical arena, the mechanisms by which CGRP triggers migraine remain uncertain. This review discusses mechanisms whereby CGRP enhances sensitivity to sensory input at multiple levels in both the periphery and central nervous system. Future studies on epistatic and epigenetic regulators of CGRP actions are expected to shed further light on CGRP actions in migraine. In conclusion, targeting CGRP represents an approachable therapeutic strategy for migraine.

Safety and efficacy of ALD403, an antibody to calcitonin gene-related peptide, for the prevention of frequent episodic migraine: a randomised, double-blind, placebo-controlled, exploratory phase 2 trial

BACKGROUND

Calcitonin gene-related peptide (CGRP) is crucial in the pathophysiology of migraine. We assessed the safety, tolerability, and efficacy of ALD403, a genetically engineered humanised anti-CGRP antibody, for migraine prevention.

METHODS

In this randomised, double-blind, placebo-controlled, exploratory, proof-of-concept phase 2 trial, patients aged 18-55 years with five to 14 migraine days per 28-day period were randomly assigned (1:1) via an interactive web response system to receive an intravenous dose of ALD403 1000 mg or placebo. Site investigators, patients, and the sponsor were masked to treatment allocation during the study. The primary objective was to assess safety at 12 weeks after infusion. The primary efficacy endpoint was the change from baseline to weeks 5-8 in the frequency of migraine days, as recorded in patient electronic diaries. Patients were followed up until 24 weeks for exploratory safety and efficacy analyses. Safety and efficacy analyses were done by intention to treat. This study is registered with ClinicalTrials.gov, NCT01772524.

FINDINGS

Between Jan 28, 2013, and Dec 23, 2013, of 174 patients randomly assigned at 26 centres in the USA, 163 received either ALD403 (n=81) or placebo (n=82). Adverse events were experienced by 46 (57%) of 81 patients in the ALD403 group and 43 (52%) of 82 in the placebo group. The most frequent adverse events were upper respiratory tract infection (placebo 6 [7%] patients vs ALD403 7 [9%] patients), urinary tract infection (4 [5%] vs 1 [1%]), fatigue (3 [4%] vs 3 [4%]), back pain (4 [5%] vs 3 [4%]), arthralgia (4 [5%] vs 1 [1%]), and nausea and vomiting (2 [2%] vs 3 [4%]). Six serious adverse events were reported by three patients and were judged to be unrelated to study drug: in the ALD403 group, one patient had four serious adverse events and one had one serious adverse event, and in the placebo group, one patient had one serious adverse event. There were no differences in vital signs or laboratory safety data between the two treatment groups. The mean change in migraine days between baseline and weeks 5-8 was -5·6 (SD 3·0) for the ALD403 group compared with -4·6 (3·6) for the placebo group (difference -1·0, 95% CI -2·0 to 0·1; one-sided p=0·0306).

INTERPRETATION

No safety concerns were noted with an intravenous dose of ALD403 1000 mg. This study also provides preliminary evidence for the efficacy of ALD403 in the preventive treatment of migraine in patients with a high monthly frequency of migraine days.

FUNDING

Alder Biopharmaceuticals.

Tapentadol inhibits calcitonin gene-related peptide release from rat brainstem in vitro

We have previously developed an in vitro model of rat brainstem explants. The latter release sizable amounts of calcitonin gene-related peptide (CGRP); basal release can be stimulated by such secretagogues as high KCl concentrations, veratridine or capsaicine. In this paradigm we investigated the activity of the analgesic agent tapentadol; the effects of tapentadol were compared to those of a classical opioid receptor agonist, morphine, and the selective noradrenaline reuptake inhibitor reboxetine. Morphine inhibited basal CGRP release, with statistical significance from 1 nM onward and maximal (-44%) inhibition at 100 μM. Morphine also inhibited K(+)-stimulated peptide release, with a significant effect from 1 μM and maximal (-39%) decrease at 100 μM, but failed to inhibit release stimulated by 10 μM capsaicin. At variance, reboxetine had no effect on baseline CGRP outflow, but was able to inhibit both K(+)-stimulated [significant inhibition from 1 μM onward and maximal (-37%) decrease at 100 μM], and capsaicin-stimulated release [significant effect from 1 μM and maximal (-31%) decrease at 100 μM]. Likewise, tapentadol had no effect on baseline CGRP release up to 100 μM, but decreased secretion stimulated by 56 mM KCl or capsaicin, with significant effects from 0.1 and 1 μM respectively; maximal inhibition over 56 mM KCl and capsaicin stimuli was -29% and -31%, respectively. Naloxone antagonized the effect of morphine, but not those of reboxetine and tapentadol, on K(+)-stimulated CGRP secretion. In conclusion the present study provides consistent pharmacological evidence that tapentadol acts as a noradrenaline reuptake inhibitor agent in this experimental model.

Cranioselectivity of sumatriptan revisited: pronounced contractions to sumatriptan in small human isolated coronary artery

BACKGROUND

Initial concerns about the coronary side-effect potential of the anti-migraine drug sumatriptan and second-generation triptans initiated cranioselectivity studies using proximal human coronary arteries. However, myocardial ischaemia may originate from both large and small human coronary arteries.

METHODS

We investigated the contractions to sumatriptan in proximal (internal diameter 2-3 mm), distal (internal diameter 1,000-1,500 μm) and small (internal diameter 500-1,000 μm) human epicardial coronary arteries and compared these with contractions in the human middle meningeal artery. Concentration response curves to sumatriptan in human coronary arteries were constructed in the absence or presence of the 5-hydroxytryptamine1B (5-HT1B) receptor antagonist SB224289 and the 5-HT1D receptor antagonist BRL15572. The effect of sumatriptan on increased cyclic adenosine monophosphate (cAMP) levels induced by forskolin in proximal and distal coronary artery segments was investigated using a biochemical assay. Western blotting was used to analyse the 5-HT1B receptor density in the human arteries.

RESULTS

Contractions in the proximal human coronary artery were significantly smaller than those in the human meningeal artery, as we showed previously. In contrast, contractions to sumatriptan in distal and small human coronary arteries were not different from those in the human meningeal artery. The 5-HT1B receptor antagonist SB224289, but not the 5-HT1D receptor antagonist BRL15572, inhibited the contraction induced by sumatriptan in the coronary arteries. Moreover, in distal, but not in proximal, coronary arteries, sumatriptan inhibited the increase in cAMP levels induced by forskolin. Contrary to our expectations, the 5-HT1B receptor expression was more pronounced in the proximal human coronary artery than in the distal and small human coronary artery.

CONCLUSIONS

Based on functional experiments in distal and small human coronary arteries, contractions to sumatriptan are not as cranioselective as previously assumed. However, the vast clinical experience with sumatriptan and other triptans has proven that these drugs are cardiovascularly safe when contraindications are taken into account.

Reactive oxygen species induce procalcitonin expression in trigeminal ganglia glia

OBJECTIVE

To examine calcitonin gene-related peptide (CGRP) gene expression under inflammatory conditions using trigeminal ganglia organ cultures as an experimental system. These cultures have increased proinflammatory signaling that may mimic neurogenic inflammation in the migraine state.

BACKGROUND

The trigeminal nerve sends peripheral pain signals to the central nervous system during migraine. Understanding the dynamic processes that occur within the trigeminal nerve and ganglion may provide insights into events that contribute to migraine pain. A neuropeptide of particular interest is CGRP, which can be elevated and play a causal role in migraine. However, most studies have overlooked a second splice product of the Calca gene that encodes calcitonin (CT), a peptide hormone involved in calcium homeostasis. Importantly, a precursor form of CT called procalcitonin (proCT) can act as a partial agonist at the CGRP receptor and elevated proCT has recently been reported during migraine.

METHODS

We used a trigeminal ganglion whole organ explant model, which has previously been demonstrated to induce pro-inflammatory agents in vitro. Quantitative polymerase chain reaction and immunohistochemistry were used to evaluate changes in messenger ribonucleic acid (mRNA) and protein levels of CGRP and proCT.

RESULTS

Whole mouse trigeminal ganglia cultured for 24 hours showed a 10-fold increase in CT mRNA, with no change in CGRP mRNA. A similar effect was observed in ganglia from adult rats. ProCT immunoreactivity was localized in glial cells. Cutting the tissue blunted the increase in CT, suggesting that induction required the close environment of the intact ganglia. Consistent with this prediction, there were increased reactive oxygen species in the ganglia, and the elevated CT mRNA was reduced by antioxidant treatment. Surprisingly, reactive oxygen species were increased in neurons, not glia.

CONCLUSIONS

These results demonstrate that reactive oxygen species can activate proCT expression from the CGRP gene in trigeminal glia by a paracrine regulatory mechanism. We propose that this glial recruitment pathway may occur following cortical spreading depression and neurogenic inflammation to increase CGRP nociceptive actions in migraine.